Cholesteric liquid-crystalline main-chain polymers (cLCPs) whose color effect is dependent on viewing angle are known and can be prepared in analogy to nematic main-chain polymers by using an additional chiral comonomer (U.S. Pat. No. 4,412,059; EP-A-0 196 785; EP-A-0 608 991; EP-A-0 391 368) or by reacting nematic main-chain polymers (LCPs) with chiral comonomers (EP-A-0 283 273). Cholesteric main-chain polymers possess a helical superstructure and are distinguished by pronounced color effects that are based on selective reflection at the helical superstructure. The precise reflection wavelength in this instance depends in particular on the pitch of the helix. The helical pitch which develops depends essentially on the proportion of the chiral comonomer, on the nature of its incorporation into the polymer, on the degree of polymerization, and on the structure of the chiral comonomer. Furthermore, many systems also show a temperature dependence of the pitch in the cholesteric phase.
Heat-reflecting platelet-shaped particles are known. They generally consist of coated mica platelets. In this case the coat thickness is selected so that the reflection is within the IR range and the platelets are colorless and transparent. Owing to the dependency of the reflection on viewing angle, such platelets do not appear colorless at every viewing angle. When viewed obliquely, they generally show an unwanted greenish color shimmer. Platelets which in addition to their IR reflection exhibit a homogeneous, hiding color effect have not been described to date.